1. Technical Field
The present disclosure relates generally to harvesting electromagnetic energy for power devices, such as, for example, an electrosurgical energy delivery device used in electrosurgical energy delivery systems for delivering electrosurgical energy to tissue.
2. Background of Related Art
Electrosurgical energy delivery systems and procedures using electrosurgical energy are designed to safely deliver electrosurgical energy to a target tissue. The equipment, the act of energy delivery or the procedures used to deliver energy may be regulated by various governmental or industrial regulations or standards, such as, for example, FCC regulations and standards for medical equipment or electromagnetic compatibility (EMC) regulations and standards to ensure that the electrosurgical equipment does not interfere with other electronic equipment. Industrial standards may be related to patient safety, such as, for example, providing sufficient electrical isolation between a generator and a patient. As such, energy generation and transmission devices are specifically designed to minimize and reduce undesirable energy delivery.
One common practice used to ensure patient safety in electrosurgical generators is to create an isolation barrier between the generator and the patient. For example, patient isolation may be provided by isolating the generator output from an earth ground. Isolation barriers may also be provided by various generally accepted circuits, such as, for example, a transformer or capacitors that would have a low impedance at one or more predetermined frequencies (e.g., 60 Hz).
While the practice of providing an electrical isolation barrier is generally effective with respect to the energy delivery aspect of the system, these techniques, practices and circuits are not as effective in providing isolation between the generator and the DC power circuits and control circuitry in the energy delivery device.
Other means of providing isolation between the generator and the powering control circuitry include providing a delivery device power source in the energy delivery device to independently power the energy delivery device. For example, a battery (or other suitable energy storage device) or a power generation source may be provided to the energy delivery device to provide complete electrical isolation between the generator and the powered control circuitry in the energy delivery device. However, providing a separate power source for the delivery device requires addition of circuitry for charge and/or charge monitoring, circuitry for preventing use when the power source is not functioning properly or not providing an adequate amount of energy for proper operation. In addition, providing an off-the-shelf or custom DC power source or power supply to provide circuit isolation is costly thereby increasing the overall per product costs.
Another system and method for providing DC power for the energy delivery device is to harvest a portion of the energy provided in the isolated energy delivery circuit to provide power to the powered control circuitry in the energy delivery device as taught hereinbelow.
Harvesting of RF energy transmitted through the air for use in powering electronic devices is extremely important in a number of fields, such as radio frequency identification (RFID) systems, security monitoring and remote sensing, among others. For example, RFID systems consist of a number of radio frequency tags or transponders (RFID tags) and one or more radio frequency readers or interrogators (RFID readers). The RFID tags typically include an integrated circuit (IC) chip, such as a complementary metal oxide semiconductor (CMOS) chip, and an antenna connected thereto for allowing the RFID tag to communicate with an RFID reader over an air interface by way of RF signals. In a typical RFID system, one or more RFID readers query the RFID tags for information stored on them, which can be, for example, identification numbers, user written data, or sensed data.
RFID tags are generally categorized as passive tags or active tags. Passive RFID tags do not have an internal power supply. Instead, the electrical current induced in the antenna of a passive RFID tag, by the incoming RF signal from the RFID reader, provides enough power for the IC chip or chips in the tag to power up and transmit a response. One passive tag technology, known as backscatter technology, generates signals by backscattering the carrier signal sent from the RFID reader. In another technology, described in U.S. Pat. Nos. 6,289,237 and 6,615,074, RF energy from the RFID reader is converted to a DC voltage by an antenna/matching circuit/charge pump combination. The DC voltage is then used to power a processor/transmitter/antenna combination that transmits information to the RFID reader at, for example, a different frequency. In either case, the area of the tag or silicon die is valuable, and therefore it is advantageous to make the most efficient use of the space thereon.
Multiple antennas can be used to generate a DC voltage from an RF signal. For example, an RFID tag may use two or more dipole antennas where the greater of the energies produced from one of the two or more dipole antennas is the one that is selected and used. This, however, is not an efficient use of tag space since the energy for the “loser” antenna is not used.
Energy-harvesting circuits, according to some embodiments of the present disclosure employ multiple antennas with each antenna structured to receive an RF signal having an RF frequency range. The RF frequency range for an antenna may be centered about a particular RF frequency or the antenna, or multiple of antennas, may collect energy from a wide range of frequencies. Matching networks and circuitry coupled to each antenna generate a plurality of DC voltage signals and the plurality of voltage signals are combined to create a combined DC voltage signal to power the RFID tag or a transponder.
RFID and/or transducers use various energy-harvesting techniques to identify and/or power a particular device wherein the tag/transducer receives an externally generated and transmitted energy signal. As such, the amount of energy generated by the energy-harvesting circuit is variable and dependant on the strength of the transducer and the distance between the RFID and transducer and transmitted energy signal.